The recent cut in rooftop solar feed-in tariffs and the looming possibility of a solar tax are sparking concern among solar power users.
In Victoria, the minimum feed-in tariff was recently reduced to 3.3 cents per kilowatt-hour. In New South Wales, IPART forecasts solar exports will be worth between 4.9 to 6.3 cents per kilowatt-hour in 2024–25, down from 7.7 to 9.4 cents in 2023/24. These changes make it crucial to optimize solar energy usage at home, especially for electric vehicle (EV) charging.
During less sunny months, charging your EV at an equal rate throughout the day is not efficient because your solar system produces more energy around noon than in the morning or afternoon. This means you might be exporting kilowatt-hours at a low feed-in price around mid-day and then buying back energy at a higher cost later in the day. Aligning your EV charging times with peak solar production can help you avoid this issue.
However, setting up an optimised solar system for EV charging can be expensive due to the need to buy special chargers, home batteries, or meters, all from the same manufacturer. And doing it all manually is a huge hassle – who has time to regularly check for the sun and adjust the charging throughout the day?
Instead, many homeowners already have all the necessary equipment through their personal computers. A PC could manage and optimise solar energy use, making additional costly equipment unnecessary, if only it had access to all the devices.
I have tried this out using the Tesla API and the Fronius Inverter API on my Mac, and successfully managed to get to ’smart charging’. Now, based on the solar output (read from the Fronius API), and if the battery is below 80%, the Mac tells the Tesla to start charging (via the Tesla API).
If a cloud passes by it will reduce the charging current and then increase it again when the sun is back. This is a highly efficient way to charge, and on a typical day in Spring would save about 5$, compared to plugging in overnight. All by making the existing equipment smarter.
There are still some limitations: Accessing detailed power inflow and outflow data from Smart Meters can be challenging, as some power companies only offer this data in CSV files, not through APIs.
So I cannot easily read the actual, real-time use of the home with software. It also only works with some manufactures, I haven’t yet gone through all of them, but from a few checks I found that many car makers are still at the stage of developing such APIs, rather than having them up and running.
These limitations underscore the need for open standards in the energy sector, and some efforts are underway globally under the banner of “Open Energy”. Future standards will be helpful, if they enable us to seamlessly integrate all our energy devices into a smart and efficient home.
I have included links to the two APIs from Fronius and Tesla below to get you started. I would also invite the community to help me check if we can further build out such software. Right now, it works for me, but it would be great if we could make it more robust, so that anyone could install it.
This could easily enhance home solar systems and make optimised EV charging more accessible. If you’re interested, live in VIC Bayside or Glen Eira, and have a similar setup to mine (Tesla, Fronius Inverter, Tesla Wall Charger, Apple Mac computer), please contact me at [email protected].
Links to technical documentation:
- Tesla API documentation:Â https://developer.tesla.com/docs
- Fronius Inverter API documentation:Â https://www.fronius.com/en/solar-energy/installers-partners/technical-data/all-products/system-monitoring/open-interfaces/fronius-solar-api-json-
I have played with the idea of integrating this into Home Assistant but kept putting it off. Also ChargeHQ did a good job of this (until they had to start charging $ due to Tesla API changes).
The Tesla app suddenly showed up Charge On Solar today – being a nice sunny day in Sydney – set it up and ran it – worked brilliantly.
Noting, of course, this needs both solar and a Tesla Powerwall (and a Tesla car!)
I had this set-up too and it worked well until Tesla restricted the API to 50 ‘free’ commands/day. It worked brilliantly up to that point. Now I have changed and I get the wall box (OpenEVSE) to change it’s available amps. This works as well also.
You just need a smart EV charger. I have a Zappi and it lets me choose between charging flat out or two options that prioritise solar use. The downside is that it cost $2750 installed. I’m in Victoria so using my own solar to charge is better than exporting at 3.3 cents/kWhr!
I have a Wallbox and same deal. I only charge in full green (solar excess) mode.
Emhass is intended to optimise deferable loads like EV charging and hot water, as well as batteries. Through home assistant there are integrations with a number of inverters and OCPP chargers. It factors in predicted solar and pricing to optimise for cost.
You don’t even need a laptop, this can be handled with a Raspberry Pi running Home Assistant. Many modern solar inverters include an API which exposes power consumption and generation data. I setup something similar in 2022 for our house. However, I don’t use it any more as our energy plan gives free power 11am-2pm and 8c/kWh from midnight to 6am. Even with 3c FIT this still works out really nicely as we have shifted all loads to align with the free and cheap power periods. The load shifting is mostly managed by Home Assistant 🙂
Which electricity plan would that be? In regional NSW I can’t seem to find anything that has this sort of benefit.
I put between 15-20kWh into my EV every night.
As a single parent with a job, charging from solar is not an option.
I am about to spend $22k to put in solar and 16kWh battery.
I’m expecting a 6-year ROI.
But more than wanting a ROI, removing the power bill means my budget is more balanced, which means I can take the kidlettes on holidays.
Oh, and I’m not putting money into the pockets of companies that are boiling our oceans.
Or if you have a largish solar system like I do, then you don’t really need a high priced smart charger. I have a cheap $750 Tesla 3 phase charger and I just plug the car in when the suns shining and let the solar panels and the house battery do their thing. If I draw a small amount from the grid then it’s not a big deal really because there is probably already excess solar floating around in the grid to be used up.
Try evvc.io. It’s fantastic, free, open source, works with a huge range of inverters, cars, batteries.
I think you might mean evcc.io ?
Sorry, fat fingers on a phone. evcc.io is correct. My wife and I both use it all the time, and she’s most definitely not a tech nerd. It allows us to soak excess solar into the car battery . evcc.io runs very well on an old raspberry pi, and setup was a cinch.
Australian company CATCH Power are doing some amazing stuff in this space. They have a really affordable and compact meter which can control most leading inverters and batteries and has the bonus of being able to drive a contactor. Their software allows integration to a growing range of EV chargers via OCPP, and allows to you “solar track” (using excess) and set schedules for off peak rates and and use it as a remote control and prioritise a number of actions and even allow “exclusions”, for example to avoid discharging batteries when EV charging. Worth a look.
Since I am typically home in the middle of the day, if the EV needs a charge I just start it set to 8A at any time in the morning the solar is producing more than 2kW. Mostly works. Automation might be neat, if it doesn’t’t require more effort than a manual start.